1. Field of the Invention
The present invention relates to: an antimicrobial aqueous solution containing an ε-polylysine and an amphipathic antimicrobial as constituent components in amounts of microgram units relative to 1 ml of water, and its preparation method; and more particularly to an antimicrobial aqueous solution which adopts, as the amphipathic antimicrobial, monoglycerol monolaurate (which may also be called “monolaurin”) or diglycerol monolaurate in a manner to use it combiningly with an ε-polylysine and to add a sucrose monolaurate as a solubilizer into the solution, and its preparation method.
2. Description of the Related Art
Higher organisms including human species live in a manner daily exposed to a wide variety of and an extremely large number of micro-organisms, from birth to death. Such micro-organisms include good bacteria and bad bacteria, so that microfloras (habitat distribution of micro-organisms) of the higher organisms have been fluctuated within certain ranges due to influences of the environment. Further, the human species have been drastically changed in lifestyle at recent times, and the influence of the environmental changes such as due to industrial activities is coming up to the area of micro-organisms. After the latter half of the 20th century, numerous antibiotics have been found out, thereby enabling to counteract serious diseases due to pathogenic microbes. To the contrary, such antibiotics tend to be overused because they allow for counteractions to serious diseases with ease, to resultingly bring about generation of antibiotics resistant microbes, which is to be counteracted as soon as possible. Moreover, there is a problem of a group of bacteria called gram negative bacteria which are originally nonsensitive to lipophilic antibiotics. These bacteria are characterized in that, whereas gram positive bacteria each have a cell surface comprising two layers of a cytoplasmic membrane and a cell wall, the gram negative bacteria each additionally include a strong membrane called an outer membrane as an outermost layer, which outer membrane acts as a barrier against lipophilic antibiotics tending to invade the gram negative bacteria from the outside thereof. Effective substances capable of invading such gram negative bacteria, are less in amount of existence. It is said that advanced persons, who have been frequently subjected to opportunities of usage of antibiotics for many years, have internal microfloras including predominant gram negative bacteria. As an example, pathogenic bacteria of geriatric pneumonia are frequently Pseudomonas being in gram negative nature and having a strong resistance against lipophilic antibiotics, so that the medical scenes undergo difficulty in medical treatments therefor (see Non-Patent Document 1, for example).
Upon occurrence of an epidemic disease under such circumstances, passive measures are taken, such as local dispersion of an antiseptic solution, and sterilization of hands of medical professionals and workers. Unfortunately, active techniques have not been found to previously eliminate possibilities of epidemic diseases, even at present where scientific techniques have been so advanced. One of the reasons thereof is that most of antiseptic solutions also have toxicities to humans as well as residual properties, so that such antiseptic solutions are not allowed to be prophylactically dispersed. Then, attention is to be directed to a presence of those among preservatives to be used for foods and the like, which are relatively low in toxicity. However, they are generally mild in antimicrobial activity and have antimicrobial spectra different from one another. As such, expectation has been redirected to a complementary or synergistic combined system, based on a combination of multiple preservatives. Specifically, it has been disclosed that food preservatives each provided by adding a protamine to a glycerol monomiddle length fatty acid ester and an ε-polylysine, are made to have broad antimicrobial spectra against various micro-organisms (see Patent Document 1, for example). Further, food preservatives have been disclosed each containing, as active ingredients: an aliphatic monoglycerin ester of a fatty acid having 8 to 12 carbon atoms; and an ε-polylysine; (see Patent Document 2, for example). Moreover, preservatives have been disclosed each having a polylysine, and a glycerin monolaurate, i.e., monolaurin (see Patent Document 3, for example).
However, these problems including the above-mentioned problem of antibiotics resistant microbes have not been solved yet. Then, the antibacterial agents disclosed in the Patent Documents 1 to 3 have been investigated to reveal that the ε-polylysine and the monoglycerol monolaurate have antimicrobial activities which are exhibited under the requirement that these components are combined with each other and used together with protamine or glycine so as to enhance the antimicrobial effects of the combined substances. Further, although the antimicrobial effects have been obtained by using these components at higher concentrations, respectively, sufficient effects against gram negative bacteria have not been obtained yet in any of the Patent Documents.
Further, monolaurin has been restricted in usage, because of its drawbacks that monolaurin is particularly inactive against gram negative bacteria and exhibits a low water solubility. In turn, although an ε-polylysine has been and is being noticed as a rare one of substances which are active even against Pseudomonas as gram negative bacteria, it is impossible to confirm an antimicrobial reinforce effect for an amphipathic antimicrobial insofar as at a usage concentration at which the antimicrobial action of ε-polylysine is expected. This is because, cell surfaces of micro-organisms are minus charged and the ε-polylysine is plus charged, so that the ε-polylysine is attached in an extremely large amount onto surfaces of the micro-organisms. Thus, it appears that usage of ε-polylysine at a high concentration causes the bonded long molecules of ε-polylysine to cover cell surfaces of micro-organisms, so that the permeability of monolaurin through cytoplasmic membranes is obstructed and the antimicrobial activity of the monolaurin is not exhibited.
Meanwhile, since an agar impression material is provided for directly collecting a mouth impression of a patient by a hand of a dentist, strict safety is demanded legally. However, none of the preservatives usable therefor has possessed a satisfactory antimicrobial effect. Then, the present inventors have noticed a combination of an ε-polylysine with an amphipathic antimicrobial and investigated addition amounts thereof, to resultingly find out that an antimicrobial activity can be reinforced by combining an ε-polylysine with an amphipathic antimicrobial at lower concentrations of microgram units relative to 1 ml of water, respectively. The present inventors have also noticed a point that the slight water soluble monolaurin is suspended in water, and have searched for a solubilization agent of monolaurin into water (hereinafter, the solubilization agent is called “solubilizer”), thereby resultingly finding out that the monolaurin dissolves, in an amount several times its solubility in water, in such a water containing a sucrose monolaurate added therein, to attain a transparent aqueous solution to thereby further progress the antimicrobial activity. In this respect, it has been found out that, when the monolaurin is provided not in a state of suspension but in a state of complete aqueous solution, there can be obtained such a collaborated effect that the monolaurin sufficiently permeates through cell surfaces of gram negative bacteria even under the influence of ε-polylysine, to exhibit an effectiveness of the monolaurin as an antibacterial agent having a broad spectrum and to further expand the spectrum up to gram negative bacteria.
It also has been found out that the addition of sucrose monolaurate exhibits not only the solubilizing effect but also such an effect that precipitated monolaurin is not caused even after a long-term storage. It has been further found out that the same effect as monolaurin can be exhibited, even when adopting a diglycerol monolaurate at a lower concentration to be handled at microgram units relative to 1 ml of water. The present invention has been narrowly completed, based on these knowledges.
[Patent Document 1] JP7-135943A1 (Claims, paragraph [0002], and paragraph [0004])
[Patent Document 2] JP2000-270821A1 (claims 1 and 2)
[Patent Document 3] JP11-228308A1 (claims 1 and 2)
[Non-Patent Document] H. NIKAIDO and M. VAARA, Microbiological Reviews, March 1985, p 1-32